Learn Modifying Algorithms

Modifying algorithms in the C++ Standard Library are essential tools for changing the contents of containers efficiently and expressively. The most commonly used modifying algorithms include std::copy, std::replace, and std::remove.

These algorithms operate on iterator ranges, making them flexible and container-agnostic.

main.cpp


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#include <iostream>
#include <list>
#include <algorithm>

int main()
{
    std::list<int> numbers = {1, 2, 3, 2, 4, 2, 5};

    // Replace all occurrences of 2 with 99
    std::replace(numbers.begin(), numbers.end(), 2, 99);

    // Remove all elements greater than 90 using remove_if
    numbers.remove_if([](int n){ return n > 90; });

    for (int n : numbers)
        std::cout << n << " ";
}

When using containers like std::vector or std::deque, algorithms such as std::remove don’t actually delete elements. Instead, they shift the remaining ones to the front and return an iterator to the new logical end, leaving the container size unchanged. To permanently remove elements, call the container’s erase function with that iterator — a common pattern known as the erase-remove idiom.

main.cpp


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#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> numbers = {1, 2, 3, 2, 4, 2, 5};

    // Remove all occurrences of 2
    auto new_end = std::remove(numbers.begin(), numbers.end(), 2);
    numbers.erase(new_end, numbers.end());

    for (int n : numbers)
        std::cout << n << " ";
}

Note

Always pair std::remove with erase to avoid leftover invalid data at the end of the container.

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Section 3. Chapter 3

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These algorithms operate on iterator ranges, making them flexible and container-agnostic.

main.cpp


              1234567891011121314151617
            
#include <iostream>
#include <list>
#include <algorithm>

int main()
{
    std::list<int> numbers = {1, 2, 3, 2, 4, 2, 5};

    // Replace all occurrences of 2 with 99
    std::replace(numbers.begin(), numbers.end(), 2, 99);

    // Remove all elements greater than 90 using remove_if
    numbers.remove_if([](int n){ return n > 90; });

    for (int n : numbers)
        std::cout << n << " ";
}

main.cpp


              1234567891011121314
            
#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> numbers = {1, 2, 3, 2, 4, 2, 5};

    // Remove all occurrences of 2
    auto new_end = std::remove(numbers.begin(), numbers.end(), 2);
    numbers.erase(new_end, numbers.end());

    for (int n : numbers)
        std::cout << n << " ";
}

Note

Always pair std::remove with erase to avoid leftover invalid data at the end of the container.

Everything was clear?

Thanks for your feedback!

Section 3. Chapter 3